1. Field of the Invention
The present invention relates to a liquid crystal display apparatus in which high polymer is mixed in liquid crystal, a liquid crystal projector using the liquid crystal apparatus, and a method of manufacturing the liquid crystal display apparatus.
2. Related Background Art
In recent years, liquid crystal display apparatuses have been widely used in various devices because of their advantages of thin sizes, low voltage driving ability, and saved power consumption, and the like, as is representatively known from a display of a direct view type having a diagonal size exceeding 10 inches. Also, liquid crystal projectors which realize display on a larger screen by providing a liquid crystal display panel together with an optical system have come to be introduced as practically useful commercial products having high resolution and brightness, as computers have spread popularly.
Liquid crystal used in those liquid crystal panels is generally TN (Twisted Nematic) liquid crystal which achieves higher response speed and contrast in comparison with STN (Super Twisted Nematic) liquid crystal used mainly in conventional panels, so that images of higher quality can be displayed.
However, in a display apparatus using TN liquid crystal, loss of light is largely due to a polarizing plate and the brightness is therefore limited. Particularly, the drawback of the TN liquid crystal display apparatus is remarkable in case of a projection type liquid crystal display apparatus which requires high brightness.
As countermeasures against the drawback, proposals have been made as to liquid crystal display apparatuses using various liquid crystal, such as "PNLC (Polymer Network Liquid Crystal)" in which TN liquid crystal is dispersed in a liquid crystal continuous phase or a sponge-like polymer network, a "high-polymer/liquid crystal composite film" capable of forming a display of a large screen by using an electro-optic effect accompanying light diffusion without using a polarizing plate, or "polymer dispersed liquid crystal" having a structure in which spherical liquid crystal grains are dispersed in a high-polymer matrix between transparent electrode and liquid crystal molecules are oriented along a wall surface of the high-polymer matrix within the grains in the following manner. Specifically, incident light is diffused when a difference exists between the average refractive index of the liquid crystal grains and the refractive index of the high-polymer matrix. As the refractive indexes is increased when a voltage is applied to the high-polymer dispersed cell, liquid crystal is released from restrictions from the wall surface of the high-polymer matrix, to be oriented to be vertical to the surfaces of the transparent electrodes. When the refractive index of the high-polymer matrix is close to the refractive index of the liquid crystal molecules in the short-axis direction of the molecules, incident light is transmitted without being dispersed.
The PNLC is provided as a type of liquid crystal in which light is transmitted at a high transmit rate by making the refractive index of TN liquid crystal be substantially equal to the refractive index of the polymer network when a voltage is applied, while incident light is diffused to produce black by a difference between the refractive index of the TN liquid crystal oriented randomly and the refractive index of the polymer network when no voltage is applied. A display apparatus using the PNLC does not use a polarizing plate, and therefore essentially realizes display with a higher light use efficiency, i.e., brighter display than a TN liquid crystal display apparatus. These phenomena and applications are common to the "high-polymer/liquid crystal composite film" and the "polymer dispersed liquid crystal".
In order to more advantageously use the high light use efficiency of the "polymer network liquid crystal" and the like, it is effective that the active matrix substrate is of a reflective type. Since a reflective type substrate can be embedded below a reflective electrode to shield light, the aperture can be increased to be close to 100%, resulting in a potential that the light use efficiency is not decreased unlike a transparent type even when the pixel size is reduced.
In case of manufacturing a liquid crystal display apparatus using "high-polymer/liquid crystal composite film", "polymer dispersed liquid crystal", or "polymer network liquid crystal" of a reflective type, an active element is embedded below a reflective electrode with respect to a reflective type substrate and high-polymer, and liquid crystal are injected and sealed between the substrate and a transparent electrode. Thereafter, ultraviolet light (UV) is irradiated thereon, and thus, a liquid crystal panel is prepared.
In particular, a method of manufacturing the (polymer dispersed liquid crystal" is described in Japanese Patent Laid-open Application No. 5-61016. According to this publication, an acrylate-based ultraviolet-polymerized composite material (using a light-polymerization starting agent of DAROQUA (phonetic translation) 1116 available from Merck & Co., Inc.) and a liquid crystal composite material (E8 available from BDH-SHA (phonetic translation)) are uniformly dissolved and injected into glass cell having an ITO electrode. Thereafter, ultraviolet light is irradiated thereon (at 1 mW for 500 seconds), thereby to prepare the polymer dispersed liquid crystal (PDLC) cell. The grain diameter of the liquid crystal composite material in the PDLC material is set to 0.1 to 10 .mu.m which is adjusted by the content of the liquid crystal composite material. That is, a liquid crystal composite material of 65 to 75 weight % is used with respect to a total weight of the high-polymer matrix and the liquid crystal composite material, to mix samples having different grain diameters.
However, in case of a conventional liquid crystal panel using ultra-violet irradiation, it has been found that uneven display occurs. Particularly, in case of irradiating ultra-violet light of parallel light onto the entire surface of liquid crystal area, there appears a phenomenon that the reflection light amount decreases concentrically from the center portion of the liquid crystal panel to the peripheral portion thereof, i.e., the transmittance rate decreases. In case of a color three-plate type, irregular color appears concentrically. These drawbacks are caused by unevenness of the polymerization condition or unevenness of liquid crystal grain diameters, and are estimated to be due to a stress during polymerization. Another factor is estimated to be that an influence from a seal differs in accordance with a distance from the seal during polymerization.
In addition, it has been found that there is a problem concerning the stability of liquid crystal. That is, the liquid crystal phase lacks the stability because of an existence of a non-reactive liquid crystal phase exists during preparation using ultraviolet light.
A liquid crystal display apparatus into which liquid crystal has been injected will be explained with reference to a cross-section shown in FIG. 5. The applicant filed Japanese Patent Application No. 7-186473 concerning a method of manufacturing an active matrix substrate. The active matrix substrate is constructed as follows. A lower portion of liquid crystal 214 is comprised of an n-type silicon semiconductor substrate 201 having an impurity density of 10.sup.15 cm.sup.-3 or less, LOCOS 202, a PWL 203 as a p-type impurity region having an impurity density of about 10.sup.16 cm.sup.-3, an NLD 206 as an n-type impurity region having an impurity density of about 10.sup.16 cm.sup.-3, source and drain regions 207 and 207' having an impurity density of about 10.sup.19 cm.sup.-3, an AI electrode 209, a PSG 211, an SiN 210, and a pixel electrode 213.
Next, an upper portion of the liquid crystal 214 is comprised of a transparent substrate 220, a color filter 221, a black matrix 222, and a common electrode consisting of an ITO or the like. However, the color filter 221 which does not transmit ultra-violet light and the black matrix 222 are not used to achieve the object of the present invention, and layers for these components are not required. This is because the active matrix substrate adopted in the present invention uses one sheet per color and the color filter of the present invention does not transmit ultra-violet light. Therefore, to achieve the object of the present invention, the upper portion of the liquid crystal 214 may have a structure comprised of a transparent substrate 220 made of glass or the like on which a transparent electrode is vapor-deposited on the side facing the liquid crystal 214 or a structure comprised of a common substrate 223 and a transparent substrate 220. Note that color filters and a black matrix must allow ultraviolet light to be transmitted to some extent, in case of adopting a liquid crystal display apparatus for a RGB matrix. In the active matrix substrate having a structure as described above, the surfaces of pixel electrodes 213 are flat and smooth, and insulating layers are embedded in clearances between adjacent pixel electrodes, resulting in an advantage in that the entire surface is not concave or convex but is flat and smooth.
A plan view of the liquid crystal apparatus will be explained with reference to FIG. 6. This figure shows a relationship between a seal structure and a panel structure. References 51, 52, 53, and 54 respectively denote a seal portion, an electrode pad, a clock buffer circuit, and an amplifier. The amplifier 54 is used as an output amplifier for an electric inspection of a panel. References 55, 56, and 57 respectively denote an Ag paste portion for obtaining an electric potential of an opposite electrode, a display portion, and a peripheral circuit portion including, for example, vertical and horizontal shift registers (HST and VSR) and the like. As shown in FIG. 6, circuits are arranged to have a small total chip size both inside and outside the seal. Although leads from the pad are concentrated at one side of edges of the panel in this embodiment, leads can be extracted from both sides of longer edges of the panel or from sides of more edges thereof, resulting in an advantage when responding to a high-speed clock.